Continuous roll casting of ferrous and non-ferrous metals

ABSTRACT

A method of continuously casting metal strip, as well as an apparatus for carrying out the process, wherein the process includes the steps of: providing a pair of casting rolls operating at a selected rotational speed and the two casting rolls being spaced apart from each other at a pre-selected distance; introducing molten metal between the two casting rolls; monitoring the separation force exerted on the two casting rolls by the molten metal, and adjusting the rotational speed of the two casting rolls in response to the magnitude of the separation force wherein the rotational speed of the two casting rolls is reduced when the separation force is below a lower value and the rotational speed of the two casting rolls is increased when the separation force is above an upper value; and processing the strip by removing any shape defects therein.

CROSS-REFERENCE TO EARLIER FILED PATENT APPLICATIONS

This patent application is a divisional of co-pending U.S. patentapplication Ser. No. 11/036,253 filed Jan. 14, 2005 by Samuel F.Savariego and entitled CONTINUOUS ROLL CASTING OF FERROUS ANDNON-FERROUS METALS. Applicant hereby claims the benefit of the earlierfiled co-pending U.S. patent application Ser. No. 11/036,253 filed Jan.14, 2005 by Samuel F. Savariego and entitled CONTINUOUS ROLL CASTING OFFERROUS AND NON-FERROUS METALS, which claimed the benefit of earlierfiled Provisional Patent Application No. 60/536,383 filed by Samuel F.Savariego on Jan. 14, 2004 for CONTINUOUS ROLL CASTING OF FERROUS ANDNON-FERROUS METALS.

BACKGROUND

This invention is related to metal working machinery and processes, andmore particularly, to improvements in an apparatus for the, as well asthe process of, continuous roll casting of ferrous and non-ferrousmetals. In this regard, Sir Henry Bessemer first conceived the conceptof continuous roll metal casting in the year 1853. Since then there havebeen a number of developments in continuous roll metal castingtechnology.

One such area of development pertains to a hot rolling casting process.In the hot rolling casting process, molten metal is fed into the bitebetween a pair of counter-rotating cooled rolls wherein solidificationis initiated when the metal contacts the rolls. Solidification prior tothe roll nip, or point of minimum clearance between the rolls, causesthe metal to be deformed, or hot rolled, prior to exiting the rolls as asolidified sheet.

While the hot rolling casting process has provided a number of benefits,there remains a desire to improve upon such a process in a number ofways. One such area of improvement concerns the number of steps thathave been necessary to produce a steel coil using the hot rollingcasting method. Heretofore, the typical hot rolling process comprisedthe steps of: (1) casting of the molten metal, (2) hot rolling the castmaterial into sheet, (3) pickling the hot rolled sheet so as to removesurface skin, (4) cold rolling the pickled sheet, (5) cleaning the coldrolled sheet, (6) annealing the cleaned cold rolled sheet and, (7)remove shape defects of the rolled sheet. As can be appreciated, eachprocess step adds an expense to the overall cost of production. Hence,it would be highly desirable to provide an improved apparatus andprocess for the continuous roll casting of metals that would not need asmany steps as heretofore required with known twin roll casting process.More specifically, it would be highly desirable to provide such animproved apparatus and process that eliminates the steps of coldrolling, cleaning and annealing.

Another area of improvement concerns the ability to produce a cast metalstrip that exits the casting rolls wherein the cast metal strip exhibitsa consistent and predetermined thickness. It would thus be highlydesirable to provide an improved apparatus and process for thecontinuous roll casting of metals that would produce a cast metal stripexiting the casting rolls that exhibits a consistent and predeterminedthickness.

In the hot rolling casting process it is important to provide anapparatus, as well as a process, that results in the least number of (oressentially completely eliminates the) physical defects in the hotrolled strip. After the hot rolled strip has been pickled and the skinremoved and the skin passed so as to provide a cold rolled-like finish,the roll is being wound around a precision mandrel and simultaneouslysubmitted to reversed bends as to elongate 80% of the grain of thesteel. The Precision (deflection free) mandrel then detects the part ofthe strip with shorter grains and elongate the shorter grain portion ofthe strip so that all grains are of equal lengths. During the windingprocess, the metal strip is subjected to high tension as well as beingsimultaneously subjected to reverse bends. Any defects in the stripwhile being subjected to this process can result in certain undesirableconditions. Thus, it would be highly desirable to provide an improvedapparatus and process for the continuous roll casting of metals thatwould produce a metal strip that exhibits a consistent thickness andshape.

For example, if there is any non-uniformity in the strip thickness orunequal length in the grains of the strip as the material is beingsubjected to reverse bending to a predetermined amount and then woundaround the mandrel, tension forces are exerted on the strip. If themagnitude of the tension forces on the strip exceeds the yield strengthof the material of the strip as it is being subjected to the reversebends, then the shorter grains of the strip will elongate to the samelength as all the other grains, and this will result in a strip that isfree of defects. It can thus be appreciated that it would be highlydesirable to provide an improved apparatus and process for thecontinuous roll casting of metals that would monitor and control theelongation of the strip so that the entire cross section of the strip iselongated by a given preset amount thereby eliminating all shape defectswherein the strip does not exhibit defective conditions.

Another example of defects heretofore found in strip steel is edgewaves. More specifically, this edge wave condition is caused because thegrains on the edges of the strip are longer (or thinner) than the grainson the center of the strip so that the grains in the center of the stripare thicker. As the material is wound about the precision drum andsimultaneously being subjected to reverse bends so that the built-up ofthe layers causes the tension on the thicker part of the strip (i.e.,the center of the strip) to be higher than the tension on the thinnerpart of the strip (i.e., the edge portions).

Keeping in mind that the tension is assisted by the reverse bendingrolls, as the winding process continues the tension on the thicker stripbecomes greater than what the entire cross section of the strip canwithstand so that the thicker part of the cross section elongates theshort grains, as it tries to travel at a higher peripheral speed thanthe thinner part, is first elongated and then the elongation extendstoward the edges of the strip until the total cross section of the stripis elongated and monitored to insure that all grains are of equallength. It can thus be appreciated that it would be highly desirable toprovide an improved apparatus and process for the continuous rollcasting of metals that would monitor and control the elongation of thestrip so as to essentially eliminate the condition of edge waves.

As still another example of defects heretofore found in steel stripthere is the condition known as center buckle or oil can or cross bow.These defects are caused because the grains on the middle part of thestrip are longer (thinner) than the grains on the edges of the strip(thicker). As the material is subjected to reverse bends so that 80% ofthe cross section of the grains are elongated and then wound about theprecision drum, the shorter grains are subjected to higher tension andare elongated so that all grains are of equal length.

Keeping in mind the assistance provided by the reverse bending rolls,the tension on the strip is greater than what the entire cross sectionof the strip can withstand, the thicker part of the cross section, as ittries to travel at a higher peripheral speed than the thinner part, isfirst elongated and then the elongation extends, beginning at the edgesof the strip and then moving toward the center of the strip, until thetotal cross section of the strip is elongated. It can thus beappreciated that it would be highly desirable to provide an improvedapparatus and process for the continuous roll casting of metals thatwould monitor and control the elongation of the strip so as toessentially eliminate the condition of center buckle or oil can or crossbow.

As yet another example of defects heretofore known in steel strip is thecondition known as camber. The condition of camber is caused because thegrains of one edge of the strip is longer (thinner) than the grains ofthe opposite edge of the strip. The edge of the strip where the grainsare shorter (thicker), as the material is wound about the precisiondrum, the built-up of the layers causes the tension on the side of theshorter grains of the strip to be higher than the tension on the longeredge of the strip.

Keeping in mind the assistance provided by the reverse bending rolls,the shorter (thicker) edge of the strip is elongated first. Then theelongation of the strip, progressively move from the thicker to thethinner edge of the strip until the entire cross section of the strip iselongated a predetermined amount. It can thus be appreciated that itwould be highly desirable to provide an improved apparatus and processfor the continuous roll casting of metals that would monitor and controlthe elongation of the strip so as to essentially eliminate the conditionof camber.

SUMMARY

In one form thereof, the invention is a method of continuously castingmetal strip comprising the steps of: providing a pair of rotatingsleeves which are internally water cooled via a stationary chamberoperating at a selected rotational speed and the two casting rolls beingspaced apart from each other at a pre-selected distance; introducingmolten metal between the two casting rolls: monitoring the separationforce exerted on the two casting rolls by the molten metal, andadjusting the rotational speed of the two casting rotating sleeves inresponse to the magnitude of the separation force wherein the rotationalspeed of the two rolls is reduced when the separation force is below alower value and the rotational speed of the two rolls is increased whenthe separation force is above an upper value.

In another form thereof, the invention is a method of continuouslytreating a moving metal strip, the method comprising the steps of:providing a mandrel driven by a motor for receiving the metal strip;providing a reverse bending roll station that engages the metal stripupstream of the mandrel; providing and equalizer roll assembly upstreamof the reverse bending roll station; providing an upstream strip speedmonitor located upstream of the reverse bending roll station anddownstream of the equalizer roll assembly whereby the upstream stripspeed monitor monitors the speed of the strip as it enters the reversebending station; providing a downstream strip speed monitor locateddownstream of the reverse bend station whereby the downstream stripspeed monitor monitors the speed of the strip as it exits the reversebending station; and controlling the tension exerted on the metal stripby the equalizer roll assembly as a function of the difference betweenthe speed of the strip entering the reverse bending station and thespeed of the strip exiting the reverse bending station.

In yet another form thereof, the invention is an apparatus forcontinuously treating a moving metal strip. The apparatus includes amandrel driven by a motor whereby the mandrel receives the metal stripin a coil. There is a reverse bending roll station positioned upstreamof the mandrel whereby the reverse bending station engages the metalstrip. The apparatus includes an equalizer roll assembly locatedupstream of the reverse bending roll station. There is an upstream stripspeed monitor located upstream of the reverse bending roll station anddownstream of the equalizer roll assembly so as to monitor the speed ofthe strip as it enters the reverse bending station, and a downstreamstrip speed monitor located downstream of the reverse bend station so asto monitor the speed of the strip as it exits the reverse bendingstation. The apparatus further includes a controller operativelyconnected to the equalizer roll assembly so as to control the tensionexerted on the strip by the equalizer roll assembly as a function of thedifference between the speed of the strip entering the reverse bendingstation and the speed of the strip exiting the reverse bending station.

BRIEF DESCRIPTION OF THE DRAWINGS

The following is a brief description of the drawings that form a part ofthis patent application:

FIG. 1 is a mechanical schematic view of the portion of the processapparatus utilized to correct physical defects in the steel strip;

FIG. 2A is an isometric view of a metal strip that exhibits the edgewave condition wherein the grains on the edges are longer (thinner) thanthe grains in the center of the strip;

FIG. 2B is a top view that shows the operation of the equalizer stationthat addresses the edge wave condition;

FIG. 3A is an isometric view that illustrates a metal strip thatexhibits the center buckle (or oil can or cross bow) condition whereinthe grains in the middle part of the strip are longer (thinner) than thegrains on the edges of the strip;

FIG. 3B is an end view of the metal strip that exhibits the condition ofcenter buckle (or oil can or cross bow) condition;

FIG. 3C is a top view that shows the equalizer station that addressesthe center buckle (or oil can or cross bow) condition;

FIG. 4A is an isometric view that illustrates a metal strip thatexhibits the camber condition wherein the grains on one edge of thestrip are longer (thinner) than the grains in the opposite edge of thestrip;

FIG. 4B is a view that shows the equalizer station that addresses thecamber condition;

FIG. 5A is a side view of the casting station of the apparatus;

FIG. 5B is a rear view of the casting station of the apparatus;

FIG. 6A is a cross-sectional view of one casting roll in the castingstation illustrating the entrance and exit of the cooling water into andout of the casting roll;

FIG. 6B is a schematic view illustrating the control arrangement for thesupply of cooling water to the casting rolls in the casting station;

FIG. 7A is a schematic view of the casting station that includes alinear transducer and load cell and casting roll and an enlargedcross-sectional view of the casting roll wherein the cross-section is ofthe casting roll in FIG. 6A;

FIG. 7B is a schematic view showing the controlling of the relativepositioning of the rolls with respect to each other in the castingstation;

FIG. 8 is a schematic view that illustrates the steps that comprises thecomplete hot rolling casting process;

FIG. 9 is a longitudinal cross-sectional view of the mandrel of theequalizer station of the fist specific embodiment of the invention;

FIG. 10 is transverse cross-sectional view of the mandrel of FIG. 9showing the mandrel in a contracted condition; and

FIG. 11 is transverse cross-sectional view of the mandrel of FIG. 9showing the mandrel in an expanded condition.

DETAILED DESCRIPTION

Referring to the drawings, this invention provides an improvedapparatus, as well as an improved process, for the continuous rollcasting of ferrous and non-ferrous metals. As will be describedhereinafter, the present invention provides an improvement in theprocess of continuous roll metal casting by synchronizing of thesolidification of the molten metal with the rotational speed of thecasting rolls and the rate of cooling of the casting rolls. In otherwords, in order to improve the quality of the cast metal exiting thecasting rolls in the casting station, one controls the rotational speedof the casting rolls and the temperature of the casting rolls via therate of cooling of the casting rolls. This is achieved by monitoring theseparation forces exerted on the casting rolls by the molten metal viaprecision load cells operatively connected to the casting rolls. Therotational speed and rate of cooling of the casting rolls and thencontrolled in response to the magnitude of the separation forces.

In this arrangement of the casting station, one casting roll is mountedin a fixed position and the other casting roll is movable on precisionslides located at each end of the casting roll. Linear transducers arelocated under the slides. The linear transducers register the positionof the movable casting roll in reference to the fixed casting roll.Initially the casting rolls are positioned so that the distance betweenthe two casting rolls is equal to the desired strip thickness. Apre-established value for the required separation force is entered intothe system computer. The load cells then provide the actual value of theseparation forces exited on the casting rolls as the strip is cast. Thevalue of the separation force is provided to the system computer so thatif the separation force varies from the pre-selected value (or range),the computer controls the motors that drive the casting rolls so as tochange (or vary) the rotational speed to maintain the separation forceat the desired pre-established value (or range).

Still referring to the casting station, the two casting rolls areintensively and continuously cooled. The temperature of the incomingcooling water to each casting roll and the exiting cooling water fromeach casting roll is continuously monitored and those values fed intothe system computer. The computer then controls the flow rate of coolingwater to the casting rolls so that a calculated (or desired) temperaturegradient between the incoming water and exiting water is maintained. Ifthe temperature gradient is too low, then the flow rate of cooling wateris trimmed down and if the temperature gradient is too high, then theflow rate of cooling water is trimmed up from the pre-established andcalculated value.

After the strip has been cast, it is hot reduced by two hot strip millswhich are located immediately in tandem. After the Hot Rolling Stand, anx-ray gauge monitors the output thickness of the second stand and via aclosed loop controls, the required changes are executed in order toproduce a high quality strip of the desired precise thickness and shape.

Another aspect of the invention is a device to correct all physicaldefects. In this specific embodiment, such a device to correct allphysical defects is embodied in an equalizer station.

As hot rolled strip, which has been pickled and the skin passed toprovide a cold rolled-like finish, is being wound around a precisionmandrel, the strip is subjected to high tension as it is simultaneouslysubjected to reverse bends, if there is any non-uniformity on the stripthickness or unequal length in the grains of the strip, as the materialis being would around the mandrel, if the tension value on the stripexceeds the yield strength of the strip as is being subjected to thereverse bends, then the shorter grains of the strip will elongate. Byproviding a device (i.e., the equalizer station which includes themandrel described hereinafter) to monitor and control the elongation,then when the entire cross section of the strip is elongated by a givenpreset amount, all shape defects are eliminated. The shape correctiondevice (i.e., the equalizer station) guarantees a camber free product.

Referring to the drawings and especially FIG. 5A through FIG. 7B, in oneaspect, the invention is a method of continuously casting metal strip(as well as an apparatus for carrying out this process) by introducingmolten metal between two casting rolls (24, 26) that comprise part ofthe casting station. The casting rolls (24, 26) are turning in oppositedirections and the casting rolls are continuously and intensively cooledby circulating water. Two side plates are tightly fitted against theturning casting rolls (24, 26) in order to form a sort of mold thatcontains the molten metal.

One casting roll 26, i.e., the adjustable casting roll, is preciselyadjusted in relation to the other casting roll 24 to a dimension (ordistance) between the casting rolls (24, 26) that is equal to thedesired thickness of the strip (30) to be cast. Load cells (34, 36) aremounted on each end and under the slide of the adjustable casting roll26. These load cells (34, 36) monitor the separation forces between thetwo casting rolls (24, 26), i.e., the separation force exerted on thecasting rolls (24, 26) by the molten metal.

If during the casting process the casting rolls (24,26) are turning(i.e., rotating) too fast, the load cells (34,36) will register a lowseparation force in that the separation force is below a pre-selectedlower limit. A signal that indicates a too fast rotational speed (i.e.,the casting rolls are rotating to fast) will be sent to the systemcomputer (termed speed control in FIG. 7B) 50. The system computer 50will then operate to reduce the speed of the motors that drive thecasting rolls 24, 26. By reducing the rotational speed of the castingrolls, the separation force will be increased to an acceptable level.

If the casting rolls 24,26 are turning (i.e., rotating) too slow, thenthe load cells 34,36 will indicate a high separation force in that theseparation force is above a pre-selected upper limit. A signal thatindicates a too slow rotational speed (i.e., the casting rolls arerotating too slow) will be sent to the system computer 50. The systemcomputer 50 will then operate to increase the speed of the motors thatdrive the casting rolls. By increasing the rotational speed of thecasting rolls, the separation force will be decreased to an acceptablelevel.

As can be appreciated, the load variations are continuously monitored bythe system computer. The magnitude of the separation force registered bythe load cell results in the rotational speed of the casting rolls beingeither trimmed (or controlled or adjusted) up or down. By adjusting therotational speed of the casting rolls, the magnitude of the separationforce is maintained within a pre-selected range of values.

Referring especially to FIGS. 6A and 6B, the rate of flow of coolingwater to the casting rolls (24, 26) is trimmed (or controlled oradjusted) as a function of the magnitude of the separation force exertedon the casting rolls by the cast metal registered by the load cells. Thewater temperature of the exiting water from the casting rolls iscontinuously monitored by the thermocouple. The difference between thesewater temperatures is the temperature gradient between the temperatureof the water that enters and exits the casting rolls. This gradient iscompared to the separation force of the two casting rolls. If theseparation force as registered by the load cells tends to increase, orconsequently if the separation force tends to decrease, then thisinformation is fed into the system computer that controls the pump sothat the flow rate is trimmed accordingly to match the calculated andempirical value for the separation force in the recipe menu of thesystem computer.

More specifically and as illustrated in the schematic FIG. 6B, if theload cells indicate that the separation force is too low, then a signalis sent to the computer (50) that controls the flow rate of coolingwater to the casting rolls for increased cooling of the metal. Morespecifically, if the load cells indicate that the separation force istoo high, then a signal is sent to the computer (50) that controls theflow rate of cooling water to the casting rolls for decreased cooling ofthe metal.

In looking at the overall process, the system computer will compare theempirical values on the recipe menu and will set the three variablesreferred to above, i.e., the rotational speed of the casting rolls, thetemperature gradient of the cooling water supplied to the casting rolls,and the separation force, so that the rate of rotation of the castingrolls and the flow rate of the cooling water precisely match (orcorrelate to) the desired separation force between the two castingrolls.

No where in the process of this invention is the strip thicknessmeasured as it is being cast. The precise positioning of the castingrolls (including the rotational speed of the casting rolls), themonitoring of the separation force, and the controlled flow of coolingwater provides for an accurate as cast thickness of the strip. As can beappreciated, the various input data (e.g., separation force, castingroll rotational speed and cooling water temperature gradient) is fedinto the system computer whereby the system computer controls thecasting roll rotational speed and cooling water temperature gradient.

The system of this invention is differentiated from other steel systemsthat are available in the market produced by conventional processes thatincludes the following steps: (1) casting, (2) hot rolling, (3)pickling, (4) cold rolling, (5) cleaning and (6) annealing. The processof the invention skips (i.e., omits) steps (4), (5) and (6), and theprocess of the invention produces a precise metal strip with a coldrolled surface finish that is dead flat and camber free. At the sametime, the process significantly reduces production cost of a productthat is a substitute for cold rolled steel produced by conventionalmethods. Another great advantage of the process is that it saves energy.

The finishing process, exclusive to this system, subjects the pickled(oxide is removed) and skin passed (smooth cold rolled finished surface)metal strip to a process so as to equalize the grains in the strip(exclusive process). This step is performed at an equalizer station. Bysubjecting the metal strip to the grain equalization step, the processof the invention removes all possible shape defects from the strip,including camber. It should be appreciated that the camber defect is adefect that is ever present in all steels produced by other methods,except for the present process.

Referring to the drawings and especially FIG. 1, the shape correctiondevice to correct all physical defects includes: a device to inducetension on the strip, and a device to subject the material to reversebends, and a precision drum designed so that when the material issubjected to high tensions, the shaft supporting the drum does notdeflect. As mentioned in the Background hereinabove, thin flat rolledsteel commonly has some or all of the following physical shape defectsthat are discussed hereinafter.

One such physical shape defect is a condition known as edge waves. Asshown in FIG. 2A, this condition is caused because the grains on theedges of the strip are longer (thinner) than the grains on the center ofthe strip (thicker). As the material is wound about the precision drum,the built-up of the layers causes the tension on the thicker part of thestrip to be higher than the tension on the thinner part. Assisted by thereverse bending rolls, the tension is greater than what the entire crosssection of the strip can withstand, the thicker part of the crosssection, as it tries to travel at a higher peripheral speed than thethinner part, is first elongated and then the elongation extends towardthe edges of the strip, until the total cross section of the strip iselongated.

The amount of elongation is controlled by the roller assembly of theequalizer station. In operation, there are two speed measuring devices,one located in front (i.e., upstream) of the bending rolls and onelocated immediately after (i.e., downstream) of the bending rolls. Whenthese speed measuring devices sense a difference in the speed of thestrip, a signal is sent to the system computer (50) so as to control theprecision mandrel whereby the shape defects are corrected by applyingmore tension in one area of the strip, i.e., in the center of the strip,than others. Although the operation of the mandrel will be described inmore detail hereinafter, very briefly, the mandrel can selectivelyexpand its diametrical dimension so as to exert an additional tension onthe region or area of the strip that exhibits the shorter grains wherebythe result is that all of the grains are of equal length which meansthat the strip is flat.

Another such physical shape defect is known as center buckles, or oilcan or cross bow. FIG. 3A is an isometric view that shows these defects,which are caused because the grains on the middle part of the strip arelonger (thinner) than the grains on the edges of the strip (thicker). Asthe material is wound about the precision drum, the built-up of thelayers causes the tension on the thicker part of the strip to be higherthan the tension on the thinner part. Assisted by the reverse bendingrolls, the tension is greater than what the entire cross section of thestrip can withstand, the thicker part of the cross section, as it triesto travel at a higher peripheral speed than the thinner part, is firstelongated and then the elongation extends, beginning at the edges of thestrip and then moving toward the center of the strip, until the totalcross section of the strip is elongated.

As described above, the amount of elongation is controlled by the rollerassembly of the equalizer station. If the two speed measuring devicessense a difference in the speed of the strip, a signal is sent to thesystem computer so as to control a precision mandrel whereby the shapedefects are corrected by applying more tension in the area of the edgesthan others. Although the operation of the mandrel will be described inmore detail hereinafter, very briefly, the mandrel can selectivelyexpand its diametrical dimension so as to exert an additional tension onthe region or area of the strip that exhibits the shorter grains wherebythe result is that all of the grains are of equal length which meansthat the strip is flat.

Another such physical shape defect is known as camber. Illustrated inthe isometric drawing FIG. 4A, this is caused because the grains of oneedge of the strip is longer (thinner) than the grains of the oppositeedge of the strip. The edge of the strip where the grains are shorter(thicker), as the material is would about the precision drum, thebuilt-up of the layers causes the tension on the side of the shortergrains of the strip to be higher than the tension on the longer edge ofthe strip. Assisted by the reverse bending rolls, the shorter (thicker)edge of the strip is elongated first. Then the elongation of the strip,progressively move from the thicker to the thinner edge of the stripuntil the entire cross section of the strip is elongated. Although theoperation of the mandrel will be described in more detail hereinafter,very briefly, the mandrel can selectively expand its diametricaldimension so as to exert an additional tension on the region or area ofthe strip that exhibits the shorter grains whereby the result is thatall of the grains are of equal length which means that the strip isflat.

Referring to the mandrel 100 and in particular to FIGS. 9-11, themandrell comprises an elongate body 102. There are six segments (104,106, 108, 110, 112, 114) that are tungsten carbide coated elements.These segments are operated by a series of corresponding wedges as bestshown in FIG. 9. Depending upon the condition of the strip as indicatedby the speed monitors, the mandrel 100 can be in a contracted conditionin which the diametrical dimension of the mandrel is at a minimum (seeFIG. 10). When in the contracted condition, the mandrel does not exert atension force upon the strip. Depending upon the condition of the stripas indicated by the speed monitors, the mandrel 100 can be in anexpanded condition in which the diametrical dimension of the mandrel isat a maximum (see FIG. 11). When in the expanded condition, the mandrelexerts a tension force upon the strip whereby the result is anequalization of the grains across the width of the strip.

As mentioned hereinbefore, there are two speed monitoring devices. Thesespeed monitoring devices provide a signal which is responsive to andindicative of the speed of the strip across the strip. This signal goesto a motor that drives a set of back tension rolls. This signal providesa TRIM

There is a roll caster station as shown in FIG. 5. Referring now to FIG.5B, the unique features of the roll caster station are illustrated.Computer aided simulations have been performed incorporating heattransfer analysis and calculations to provide the initial values for thefollowing parameters: (1) the separation forces between the two layersof the solidified strip that are fused together, and (2) the temperaturegradient between the cooling water at the intake and outlet of thecasting rolls. The calculated initial values are then adjusted using theempirical data that is accumulated in actual operation.

The position of the casting rolls are not changed during operation. Thedistance of separation, that determines the thickness of the strip thatis being produced is obtained by two (2) anti-backlash jactuators thatare driven by means of a high torque hydraulic motor. The actualposition of the roll is then registered by a linear transducer which viaa proportional valve positions the movable roll to the precise distanceof separation from the stationary roll.

Two load cells located at the base of the anti backlash jactuators,precisely monitor the actual separation force and compares it againstthe calculated value of the separation force, then the speed of thecasting rolls is adjusted up or down, depending on the registered forceof the separation between the two rolls. This speed trim, as a functionof the separation forces, is complimented by a second speed trim that isprovided by the actual temperature gradient of the incoming versus theoutgoing cooling water.

FIG. 6B displays the cooling water flow across the roll and displays thecontrol diagram which are provided in order to monitor and control thetemperature gradient during the casting process.

FIG. 7 displays the location of the load cells and the closed loopcontrol that is used to trim the speed as a function of the separationforce during the casting process.

In operation, one possible use for this process is to produce asubstrate for Galvanizing line. Normally the substrate used to produceconstruction grade galvanized steel is full hard cold rolled steel, thefurnace must anneal the full hard material and in order to do this, thestrip has to be heated to 1472° F. (800° C.) and then cooled to thegalvanizing temperature, which is 860° F. (460° C.). If the substrate isthe product of the present invention, then the furnace does not have toanneal the steel and this creates an advantageous situation for thecustomers. In one aspect, since the product does not require annealing,the production speed does not have to be reduced as the thickness of thematerial increases. An increase in production (as much as 300%) isobtained with a reduction in energy consumption.

The patents, patent applications, and other documents identified hereinare hereby incorporated by reference herein.

Other embodiments of the invention will be apparent to those skilled inthe art from a consideration of the specification of the practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as illustrative only, and that the true spiritand scope of the invention being indicated by the following claims.

1. A method of continuously casting metal strip comprising the steps of:providing two casting rolls spaced apart from each other at apre-selected distance and operating at a selected rotational speed;introducing molten metal between the two casting rolls, monitoring theseparation force exerted on the two casting rolls by the molten metal,and adjusting the rotational speed of the two casting rolls in responseto the magnitude of the separation force wherein the rotational speed ofthe two casting rolls is reduced when the separation force is below alower value and the rotational speed of the two casting rolls isincreased when the separation force is above an upper value.
 2. Themethod of continuously casting metal strip according to claim 1 furtherincluding the steps of: supplying coolant to the casting rolls at acoolant flow rate, and adjusting the coolant flow rate to the castingrolls in response to the magnitude of the separation force
 3. The methodof continuously casting metal strip according to claim 2 wherein if theseparation force exceeds the upper value, the coolant flow rate isdecreased and if the separation falls below the lower value, the coolantflow rate is increased.
 4. The method of continuously casting metalstrip according to claim 1 further including the steps of: causingcoolant to enter and exit the casting rolls at a coolant flow rate. 5.The method of continuously casting metal strip according to claim 4further including the steps of sensing the difference between thetemperature of the coolant entering the casting rolls and thetemperature of the coolant exiting the casting rolls to define atemperature gradient.
 6. The method of continuously casting metal stripaccording to claim 5 further including the steps of: decreasing thecoolant flow rate when the temperature gradient is less than a low valueand increasing the coolant flow rate when the temperature gradient isgreater than a high value.
 7. The method of continuously casting metalstrip according to claim 5 further including the step of maintaining thetemperature gradient within a pre-selected range by adjusting thecoolant flow rate.
 8. A method of continuously casting metal stripcomprising the steps of: providing two casting rolls spaced apart fromeach other at a pre-selected distance and operating at a selectedrotational speed; introducing molten metal between the two castingrolls, monitoring the separation force exerted on the two casting rollsby the molten metal, supplying coolant to the casting rolls at a coolantflow rate, and adjusting the coolant flow rate to the casting rolls inresponse to the magnitude of the separation force
 9. The method ofcontinuously casting metal strip according to claim 8 wherein if theseparation force exceeds the upper value, the coolant flow rate isdecreased and if the separation falls below the lower value, the coolantflow rate is increased.
 10. A mandrel assembly for receiving a movingstrip so as to exert a tension upon the strip, the mandrel assemblycomprising: a deflection-free mandrel defining a generally cylindricalperipheral surface and the mandrel having a transverse dimension; themandrel being movable between and including a contracted positionwherein the mandrel presents a minimum transverse dimension so as toexert a minimum tension on the strip and an expanded position whereinthe mandrel presents a maximum dimension so as to exert a maximumtension upon the strip; and a controller operatively connected to themandrel so as to move the mandrel to a position between and includingthe contracted position and expanded position so as to exert a selectedtension on the moving strip.
 11. The mandrel assembly of claim 10wherein the mandrel includes a segment that has an exterior surface thatdefines at least a portion of the cylindrical peripheral surface of themandrel, and the segment being movable between and including acontracted position wherein the mandrel presents the minimum transversedimension and an expanded position wherein the mandrel presents themaximum dimension.
 12. The mandrel assembly of claim 10 wherein themandrel includes a plurality of the segments.
 13. The mandrel assemblyof claim 10 wherein the controller being operatively connected to aspeed monitoring means for monitoring the speed of the moving strip at apre-selected position, and the controller moving the mandrel into aselected position in response to the speed of the moving strip at thepre-selected position
 14. A method for making a metal strip comprisingthe steps of: providing two casting rolls spaced apart from each otherat a pre-selected distance and operating at a selected rotational speed;introducing molten metal between the two casting rolls whereby a metalstrip exits the casting rolls; monitoring the separation force exertedon the two casting rolls by the molten metal; providing adeflection-free mandrel driven by a motor for receiving the metal strip;providing a reverse bending roll station that engages the metal stripupstream of the mandrel; providing an equalizer roll assembly upstreamof the reverse bending roll station; providing an upstream strip speedmonitor located upstream of the reverse bending roll station anddownstream of the equalizer roll assembly whereby the upstream stripspeed monitor monitors the speed of the metal strip as it enters thereverse bending roll station; providing a downstream strip speed monitorlocated downstream of the reverse bending roll station whereby thedownstream strip speed monitor monitors the speed of the metal strip asit exists the reverse bending roll station; and controlling the tensionexerted on the metal strip as a function of the difference between thespeed of the metal strip entering the reverse bending roll station andthe speed of the metal strip exiting the reverse bending roll station.15. The method of making a metal strip according to claim 14 furtherincluding the step of adjusting the rotational speed of the two castingrolls in response to the magnitude of the separation force wherein therotational speed of the two casting rolls is reduced when the separationforce is below a lower value and the rotational speed of the two castingrolls is increased when the separation force is above an upper value.16. The method of making a metal strip according to claim 15 furtherincluding the steps of: supplying coolant to the casting rolls at acoolant flow rate, and adjusting the coolant flow rate to the castingrolls in response to the magnitude of the separation force
 17. Themethod of making a metal strip according to claim 16 wherein if theseparation force exceeds the upper value, the coolant flow rate isdecreased and if the separation falls below the lower value, the coolantflow rate is increased.
 18. The method of making a metal strip accordingto claim 15 further including the steps of: causing coolant to enter andexit the casting rolls at a coolant flow rate.
 19. The method of makinga metal strip according to claim 18 further including the steps ofsensing the difference between the temperature of the coolant enteringthe casting rolls and the temperature of the coolant exiting the castingrolls to define a temperature gradient.
 20. The method of making a metalstrip according to claim 14 wherein the mandrel having a generallycylindrical surface so as to define a diameter, and controlling of thetension exerted on the metal strip is performed by the mandrel whereinthe diameter of the mandrel increases or decreases in response to thedifference between the speed of the metal strip entering the reversebending roll station and the speed of the metal strip exiting thereverse bending roll station.